1. Field of Invention
The invention relates to a driving circuit for an active matrix type display using an electro-optical element, such as an organic electroluminescence element (hereinafter referred to as “organic electroluminescence element”), and the like. The invention further relates to a driving method of electronic device and an electronic apparatus, and to the electronic device. More particularly, the present invention relates to a driving circuit having a function for applying reverse bias to an electro-optical element to suppress the deterioration thereof, to a driving method of electronic device and an electronic apparatus, and to the electronic device.
2. Description of Related Art
It is known that a display can be realized by arranging a plurality of pixels in matrix that include an organic electroluminescence element that is one of electro-optical elements. In such a display, the organic electroluminescence element is arranged such that a laminated organic thin film including a light emitting layer is interposed between a cathode formed of a metal electrode, for example, Mg, Ag, Al, Li, and the like and an anode formed of a transparent electrode composed of ITO (indium tin oxide).
FIG. 8 shows an ordinary arrangement of a driving circuit for an active matrix type display using an organic electroluminescence element. In this figure, the organic electroluminescence element is shown as a diode 10. Further, the driving circuit 1 is composed of two transistors Tr1 and Tr2 each composed of a thin film transistor (TFT) and a capacitance element 2 for accumulating electric charge.
Herein both the transistors Tr1 and Tr2 are p-channel type TFTs. The transistor Tr1 can be controlled to be turned on and off according to the electric charge accumulated in the capacitance element 2 in the figure. The capacitance element 2 is charged by a data line VDATA through the transistor Tr2 that is turned on by setting a selection potential VSEL to a low level. When the transistor Tr1 is turned on, a current flows to the organic electroluminescence element 10 through the transistor Tr1. The continuous flow of the current to the organic electroluminescence element 10 permits the element to emit light continuously.
FIG. 9 shows a brief timing chart for the circuit of FIG. 8. As shown in FIG. 9, when data is to be written, the transistor Tr2 is turned on by setting the selection potential VSEL to the low level, whereby the capacitance element 2 is charged. This charge period is a writing period Tw in the figure. An actual display period follows the writing period Tw. In this period, the transistor Tr1 is turned on by the electric charge accumulated in the capacitance element 2. This period is shown as a display period TH in the figure.
FIG. 10 shows another arrangement of the driving circuit for the organic electroluminescence element. The driving circuit shown in the figure is written in the literature “The Impact of Transient Response of Organic Light Organic Light Emitting Diodes on the Design of Active Matrix OLED Displays” (1998 IEEE IEDM 98-875). In FIG. 10, reference numeral Tr1 denotes a driving transistor, reference numeral Tr2 denotes a charge controlling transistor, reference numeral Tr3 denotes a first selection transistor, and reference numeral Tr4 denotes a second selection transistor that is turned off during the charge period of a capacitance element 2.
As is well known, the characteristics of transistors are dispersed even if they have the same standard. Accordingly, even if the same voltage is applied to the gates of transistors, a current having a given value does not always flow through the transistors, which may cause irregular luminance and the like. In contrast, in this driving circuit, electric charge is accumulated in the capacitance element 2 based on an amount of current according to a data signal output from a current source 4. Thus, the emitting state of organic electroluminescence can be controlled based on the amount of current according to data.
Herein all the transistors Tr1 to Tr4 are P-channel type MOS transistors. The transistors Tr2 and TR3 are turned on by setting a selection potential VSEL to a low level, which causes electric charge having a value according to the output from the current source 4 to be accumulated in the capacitance element 2. Then, after the selection potential VSEL goes to a high level and the transistors Tr2 and Tr3 are turned off, the transistor Tr1 is turned on by the electric charge accumulated in the capacitance element 2 and the transistor Tr4 is turned on by a data holding control signal Vgp so that a current flows to the organic electroluminescence element 10.
FIG. 11 shows a brief timing chart as to the circuit of FIG. 10, As shown in FIG. 11, when data is to be written by the current source 4, the transistors Tr2 and Tr3 are turned on by setting the selection potential VSEL to the a low level, thereby charging the capacitance element 2. This charging period is a writing period Tw in FIG. 11. An actual display period follows the write period Tw. During the period in which the data holding control signal Vgp is set to the low level, the transistor Tr1 is turned on, and this turned-on period is a display period TH.
FIG. 12 shows still another arrangement of the driving circuit for the organic electroluminescence element. The driving circuit shown in the figure is the circuit disclosed in Japanese Unexamined Patent Application Publication No. 11-272233. In this figure, the driving circuit includes a transistor Tr1 for supplying a current from a power supply to an organic electroluminescence element 10 when it is turned on, a capacitance element 2 for accumulating electric charge for maintaining the transistor Tr1 in the turned-on state, and a charge controlling transistor Tr5 for controlling the charge of the capacitance element 2 according to an external signal. Note that when the organic electroluminescence element 10 is to emit, a potential Vrscan is maintained to a low level to turn off a charge controlling transistor Tr7. With this operation, no reset signal Vrsig is output. Note that reference numeral Tr6 denotes an adjustment transistor.
The transistor Tr5 is turned on, and the capacitance element 2 is charged by a data line VDATA through a transistor Tr6. Then, the conductance between the source and the drain of the transistor Tr1 is controlled according the charged level of the capacitance element 2, and a current flows to the organic electroluminescence element 10. That is, as shown in FIG. 13, when a potential Vscan is set to a high level to turn on the transistor Tr5, the capacitance element 2 is charged through the transistor Tr6. The conductance between the source and the drain of the transistor Tr1 is controlled according the charged level of the capacitance element 2, and a current flows to the organic electroluminescence element 10. The organic electroluminescence element 10 emits.